KFF COVID-19 Vaccine Monitor: May 2021

This KFF COVID-19 Vaccine Monitor was designed and analyzed by public opinion researchers at the Kaiser Family Foundation (KFF). The survey was conducted May 18-May 25, 2021, among a nationally representative random digit dial telephone sample of 1,526 adults ages 18 and older (including interviews from 327 Hispanic adults and 307 non-Hispanic Black adults), living in the United States, including Alaska and Hawaii (note: persons without a telephone could not be included in the random selection process). Phone numbers used for this study were randomly generated from cell phone and landline sampling frames, with an overlapping frame design, and disproportionate stratification aimed at reaching Hispanic and non-Hispanic Black respondents. Stratification was based on incidence of the race/ethnicity subgroups within each frame. Specifically, the cell phone frame was stratified as: (1) High Hispanic: Cell phone numbers associated with rate centers from counties where at least 35% of the population is Hispanic; (2) High Black: Cell phone numbers associated with remaining rate centers from counties where at least 35% of the population is non-Hispanic Black; (3) Else: numbers from all remaining rate centers. The landline frame was stratified as: (1) High Black: landline exchanges associated with Census block groups where at least 35% of the population is Black; (2) Else: all remaining landline exchanges. The sample also included 162 respondents reached by calling back respondents that had previously completed an interview on the KFF Tracking poll at least nine months ago. Another 134 interviews were completed with respondents who had previously completed an interview on the SSRS Omnibus poll (and other RDD polls) and identified as Hispanic (n = 46; including 19 in Spanish) or non-Hispanic Black (n=88). Computer-assisted telephone interviews conducted by landline (248) and cell phone (1,278, including 963 who had no landline telephone) were carried out in English and Spanish by SSRS of Glen Mills, PA. To efficiently obtain a sample of lower-income and non-White respondents, the sample also included an oversample of prepaid (pay-as-you-go) telephone numbers (25% of the cell phone sample consisted of prepaid numbers) Both the random digit dial landline and cell phone samples were provided by Marketing Systems Group (MSG). For the landline sample, respondents were selected by asking for the youngest adult male or female currently at home based on a random rotation. If no one of that gender was available, interviewers asked to speak with the youngest adult of the opposite gender. For the cell phone sample, interviews were conducted with the adult who answered the phone. KFF paid for all costs associated with the survey.

The combined landline and cell phone sample was weighted to balance the sample demographics to match estimates for the national population using data from the Census Bureau’s 2019 U.S. American Community Survey (ACS), on sex, age, education, race, Hispanic origin, and region, within race-groups, along with data from the 2010 Census on population density. The sample was also weighted to match current patterns of telephone use using data from the January- June 2020 National Health Interview Survey The weight takes into account the fact that respondents with both a landline and cell phone have a higher probability of selection in the combined sample and also adjusts for the household size for the landline sample, and design modifications, namely, the oversampling of potentially undocumented respondents and of prepaid cell phone numbers, as well as the likelihood of non-response for the re-contacted sample. All statistical tests of significance account for the effect of weighting.

The margin of sampling error including the design effect for the full sample is plus or minus 3 percentage points. Numbers of respondents and margins of sampling error for key subgroups are shown in the table below. For results based on other subgroups, the margin of sampling error may be higher. Sample sizes and margins of sampling error for other subgroups are available by request. Note that sampling error is only one of many potential sources of error in this or any other public opinion poll. Kaiser Family Foundation public opinion and survey research is a charter member of the Transparency Initiative of the American Association for Public Opinion Research.